The invention relates to an apparatus for accurately imprinting unmarked continuous foils with images of a first predetermined length wherein, after imprinting, the foil is divided into sections of a second predetermined length. The images are imprinted on the foil such that they are accurately positioned within the foil sections.
Such printing apparatus are used for example in the pharmaceutical industry. In these applications, it is important that so-called blister packages in which for example single pills are packaged are provided with an image which is accurately imprinted onto the package at a predetermined location.
Generally, the pills are disposed in a cavity formed by a deep-drawn foil of plastic or paper which is sealed by a cover foil. Imprinted onto the cover foil is an image which generally provides some information about the pill such as information regarding the timee when the pills have to be taken. It is therefore important that the information is properly printed onto the cover foil.
Because there is a need for large amounts of such blister packagings, preprinted cover foils of a large length are utilized which are usually disposed on rolls.
Although a good printing accuracy can be achieved with modern printing techniques, it is very difficult to accurately join the cover foil with the deep drawn foil such that the imprint is properly positioned over the cavities receiving the pills since any deviations may add up in the joining process. The position of the imprinted area may therefore, in time, be substantially different from the required position.
In order to be able to join the cover foil with the deep drawn foil having the pill-receiving cavities in an accurate position, the imprint on the already imprinted foils is therefore generally somewhat smaller than it is actually necessary. The length difference provided thereby is compensated for by stretching. The cover foil is pulled by a special arrangement to assume the required length. By intentionally printing the image at a length different from the actually desired length and compensating for the difference individually by stretching the cover foil, the adding of the manufacturing tolerances can be avoided, but such a procedure is quite expensive.
DE 195 00 169 A1 discloses a printing system for the double-sided imprinting of a continuous paper web, wherein between a first and a second printer an intermediate buffer arrangement is disposed for accommodating the difference of the paper advancing speeds between the first and the second printers. A detector determines the retention volume in the intermediate buffer arrangement. A printer controller stops the printing and advancing of the first printer when the retention amount exceeds a predetermined first value. The printer controller resumes the printing and paper advance by the first printer when the retention amount falls below a second value. Printing and paper advance then continue until the retention amount exceeds again the first predetermined value.
DE 34 20 304 A1 discloses an apparatus which includes several autonomous printing units that are in a position to perform different printing processes. Furthermore, the apparatus includes one or several independent units for final treatment which are in the position to perform various finishing steps such as perforating or cutting. In addition, the apparatus includes equipment for the selective control of each of these independent units in such a way that the printing and/or finishing steps are adapted to the work performed by the high speed printer. The equipment for the selective control includes sensors which recognize markings on the carrier web to be imprinted as it is moved through the high speed printer.
It is the object of the present invention to provide a printing apparatus with which a printing image can be imprinted on a foil in an accurate position without accumulation of errors and without the need for stretching the foil.